1. Field of the Invention
This invention relates to a photocurable and thermosetting liquid composition capable of forming a matte film of low gloss and more particularly to a photocurable and thermosetting composition developable with an aqueous alkaline solution and suitable for the formation of such a matte film as a solder resist and an interlaminar insulating layer of household or industrial printed circuit boards.
2. Description of the Prior Art
In recent years, owing to the trend of printed circuit boards toward patterns of growing fineness, the adhesion of solder to the resist film which occurs during the course of wave soldering forms a major cause for inducing such defects as bridges. It is commonly done in the art to form a resist film having a matte surface for the purpose of precluding such defects, thereby enhancing the resistance of the resist film to adhesion of solder during the course of wave soldering and precluding the adhesion of solder thereto. The compositions to be used for forming such matte films of this class heretofore well known to the art are such that are formed by the incorporation of various fillers such as silica and talc as a matting component.
In such a matte resist composition, however, its thixotropy increases in proportion as the amount of filler incorporated therein increases, which eventually induces the composition to emit bubbles and raise skips during the course of printing and entails a clear decline in printability thereof. Although the incorporation of the filler in the composition in a large amount gives rise to a matte surface, such a large amount of filler poses disadvantages of exerting a harmful influence on the electrical insulating properties etc. of the film to be formed.
Then, in the case of the matte resist composition using a filler of large particle diameters as a matting component, when the film is formed in a small thickness pattern, the fillers are liable to come into view through the surface of a coating film due to their large particle diameters and consequently induce infiltration of such extraneous matter as water and chemicals along the interface between the filler and the resin matrix until the surface of the substrate, which will result in deficiency in reliability of the film as in terms of resistance to chemicals and electrical insulating properties. This composition is also at a disadvantage in failing to satisfy the need for fine patterns on account of the large particle diameters of the filler.
A main object of the present invention, therefore, is to provide a photocurable and thermosetting composition which is capable of forming a matte film possessed of good properties even if it contains no filler as a matting component or contains a filler only in a small amount.
Another object of the present invention is to provide at a low cost a photocurable and thermosetting composition which excels in ability to form fine patterns, retains low gloss of the film stably, and is useful for the formation of a matte film excelling in such film properties as resistance to adhesion of solder during the course of wave soldering, resistance to chemicals, resistance to electroless gold plating, electrical insulating properties, resistance to heat, fastness of adhesion, and hardness.
To accomplish the objects mentioned above, in accordance with a first fundamental embodiment of the present invention, there is provided a photocurable and thermosetting composition for forming a matte film, which comprises (A) a photosensitive prepolymer obtained by causing a saturated or unsaturated polybasic acid anhydride to react with a hydroxyl group of an esterification product of a novolak type epoxy compound and an unsaturated monocarboxylic acid, (B) a carboxyl group-containing copolymer resin, (C) a photopolymerization initiator, (D) a diluent, and (E) an epoxy compound having at least two epoxy groups in its molecule (hereinafter referred to as a xe2x80x9cpolyfunctional epoxy compoundxe2x80x9d).
In accordance with a second embodiment of the present invention, there is provided a photocurable and thermosetting composition for forming a matte film, which comprises (A) a photosensitive prepolymer obtained by causing a saturated or unsaturated polybasic acid anhydride to react with a hydroxyl group of an esterification product of a novolak type epoxy compound and an unsaturated monocarboxylic acid, (B) a carboxyl group-containing copolymer resin, (C) a photopolymerization initiator, (D) a diluent, (E) a polyfunctional epoxy compound, and (F) an inorganic filler.
These photocurable and thermosetting compositions may contain further (G) a curing agent for epoxy resin.
As the carboxyl group-containing copolymer resin (B) mentioned above, (b-1) a copolymer of an unsaturated carboxylic acid with another compound having an unsaturated double bond, (b-2) a prepolymer obtained by causing an epoxy group-containing unsaturated compound to partially react with a carboxyl group of a copolymer of an unsaturated carboxylic acid and another compound having an unsaturated double bond, or (b-3) a prepolymer obtained by causing addition reaction of a carboxyl group-containing compound to an epoxy group of an epoxy group-containing copolymer and then causing a saturated or unsaturated polybasic acid anhydride to react with the hydroxyl group caused by the above reaction is preferred to be used. It is desirable that the ratio of the aforementioned photosensitive prepolymer (A) to the carboxyl group-containing copolymer resin (B) to be incorporated should be (A):(B)=100: about 5 to about 250, preferably (A):(B)=100:5 to  less than 100, in weight ratio.
Since the photocurable and thermosetting composition mentioned above is capable of forming a matte film which excels in such film properties as resistance to adhesion of solder during the course of wave soldering, resistance to chemicals, resistance to electroless gold plating, electrical insulating properties, resistance to heat, and hardness and is possessed of excellent fastness of adhesion to a copper foil and to various deposited layers by plating owing to microfine rises and falls in the film surface, it is useful in preparing such matte films as a solder resist and an interlaminar insulating layer in printed circuit boards. In a particularly advantageous embodiment, there is provided a printed circuit board having a resist film formed thereon from a cured and patterned resist film of the photocurable and thermosetting composition mentioned above and possessed of a 60xc2x0 gloss value of not more than about 50, preferably mot more than about 30, in the film surface in accordance with ASTM D 523-89.